Kia Forte Turbo Forum banner
1 - 20 of 88 Posts

·
Registered
Joined
·
121 Posts
Discussion Starter · #1 ·
Hi,

I have a noob and naive question. I'm planing to install an Evilla Axle Back. As far I understand, we have 2 catalytic in our exhaust system (someone can correct me on this) and to increase performance I need to work on those cats. Now, I don't want to have issues with the SMOG checks but modifying a catalytic can introduce issues during SMOG inspection (I live in CA). What can I do to increase performance from the exhaust, without compromising the SMOG inspection? If there is anything to do, would adding a SRI (short ram intake) while keeping the stock cats and the Evilla Axle Back would give me some improvements, or just noise? Sorry if these question are naive, modding a car for the first time.

Thanks for your time.
 

·
Registered
Joined
·
514 Posts
on the midpipe resides the 2nd cat.
if you gut out the inside of the cat and then install it back on this would probably pass visual inspection.
this will free up the airflow by some claims considerably. i myself am planning to do this soon.
 

·
Registered
Joined
·
1,703 Posts
the other option is to go with a high flow CAT.
 

·
Registered
Joined
·
514 Posts
anything other than stock might not pass visual right? i'm not sure here because we don't have visual checks.
 

·
Registered
Joined
·
121 Posts
Discussion Starter · #5 ·
anything other than stock might not pass visual right? i'm not sure here because we don't have visual checks.
Here in CA we have visual inspection too due to the CARB. I think it is going to be a mess dealing with the CAT due to the stupid laws we got here. I'm just ading the Axle back and the SRI only. Thanks for your input guys.
 

·
Registered
Joined
·
514 Posts

·
Registered
Joined
·
121 Posts
Discussion Starter · #8 ·
if you just punch out whats inside the second cat it can't be visually noticed but you will notice more flow.
i dunno about any exhaust tests over there but i thought i read here that our second cat isn't monitored by our car.
more info if your interested http://www.forteturbo.org/forum/19-kia-forte-turbo-performance/211-gutted-cat.html
Thanks for pointing out this thread. It seems gutting the second cat won't throw a cel neither impact in the noise, but I'm concern about SMOG and emissions. Maybe I should discuss this with the muffler guy I'm working with to modify my exhaust.
 

·
Registered
Joined
·
1,703 Posts
Thanks for pointing out this thread. It seems gutting the second cat won't throw a cel neither impact in the noise, but I'm concern about SMOG and emissions. Maybe I should discuss this with the muffler guy I'm working with to modify my exhaust.
Most likely it will. However, I think, and it is not backed up by anything, just my small brain... so I think that the second CAT is only there to backup the 1st CAT in case the first misses anything. As long as the 1st runs correctly, second is non-active.
It could be verified by measuring temperature.... the first one must be running hot and might even warming up the exhaust gases, while the second will be much colder, basically like exhaust in/out.
 

·
Registered
Joined
·
121 Posts
Discussion Starter · #10 ·
Most likely it will. However, I think, and it is not backed up by anything, just my small brain... so I think that the second CAT is only there to backup the 1st CAT in case the first misses anything. As long as the 1st runs correctly, second is non-active.
It could be verified by measuring temperature.... the first one must be running hot and might even warming up the exhaust gases, while the second will be much colder, basically like exhaust in/out.
Jumm.... If the second CAT is there to back-up the first CAT, and not to provide a second process of cleaning the emissions, then, removing the second cat won't improve or affect performance?
 

·
Registered
Joined
·
514 Posts
you can also take the midpipe off the car and to a shop to have them make a test pipe.
swap back to stock when doing inspection. this is the more ideal route for better flow imo.
i'm just gonna punch the inside of the cat for now while i get the funds later.
 
  • Like
Reactions: SXTurbo and PLP

·
Registered
Joined
·
1,703 Posts
Jumm.... If the second CAT is there to back-up the first CAT, and not to provide a second process of cleaning the emissions, then, removing the second cat won't improve or affect performance?
That's what I would think, because if the 2nd CAT was solely responsible for good cleaning of exhaust, it would be monitored, right?

Another possibility for the second CAT is simply cold start. Catalytic converters need to be hot to operate efficiently, hence on cold they are "weak", so putting two in series may solve the problem.

Just my thoughts... I never found any good explanation for the second cat when it is NOT monitored, because other systems where the second cat is monitored, they removed NOx or aid in secondary cleaning under certain conditions. Yet, there is another set of oxygen sensors.


In summary - I believe, but this is only my personal "half-educated" guess - removal (gutting) of the second CAT will NOT affect overall emission performance and WILL pass the "smog test". Assuming those tests are done when car reaches operating temperature and the first CAT works correctly.
 

·
Registered
Joined
·
238 Posts
you can also take the midpipe off the car and too a shop to have them make a test pipe.
swap back to stock when doing inspection. this is the more ideal route for better flow imo.
i'm just gonna punch the inside of the cat for now while i get the funds later.
I'd really like to know if there is any sound difference at all after you gut that second cat. I got a quote of $250.00 from a local shop to make a direct bolt in mid pipe.
 

·
Registered
Joined
·
1,703 Posts
  • Like
Reactions: SXTurbo

·
Registered
Joined
·
1,703 Posts

·
Registered
Joined
·
121 Posts
Discussion Starter · #18 ·
That's what I would think, because if the 2nd CAT was solely responsible for good cleaning of exhaust, it would be monitored, right?

Another possibility for the second CAT is simply cold start. Catalytic converters need to be hot to operate efficiently, hence on cold they are "weak", so putting two in series may solve the problem.

Just my thoughts... I never found any good explanation for the second cat when it is NOT monitored, because other systems where the second cat is monitored, they removed NOx or aid in secondary cleaning under certain conditions. Yet, there is another set of oxygen sensors.


In summary - I believe, but this is only my personal "half-educated" guess - removal (gutting) of the second CAT will NOT affect overall emission performance and WILL pass the "smog test". Assuming those tests are done when car reaches operating temperature and the first CAT works correctly.
This would make sense. But, what I've seen so far, if it doesn't affect emissions tests then, it won't have an impact in performance neither. Is it just sitting there as an extra weight?
 

·
Registered
Joined
·
1,703 Posts
But, what I've seen so far, if it doesn't affect emissions tests then, it won't have an impact in performance neither. Is it just sitting there as an extra weight?
For sure it does affect emission (makes it cleaner) but it is not monitored. And I think it might be helping in limited way. Most likely on cold only... Again - it is only my attempt to understand the system.


As for performance - it is extra restriction on the exhaust flow. Basically it creates pressure drop after the turbo. Without this extra resistance, exhaust gases would flow faster and allow the turbo to spool faster.

And just another thought. If CAT was gutted it would actually be better than regular down pipe, because the CAT box would be a small kind of chamber, kind of buffer, for sudden pressure buildup, hence allowing even faster spool.
But this one I stretched probably too far :) Exhaust flow is so high that would make no difference.
 
1 - 20 of 88 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top